Team Bridges Nanocatalyst Size Gap for Real-Time Data

COLUMBIA, S.C., and HOUSTON, June 9, 2014 — Obtaining real-time reaction information from nanocatalysts has long impeded attempts to describe them in detailed kinetic behavior.

But a team from the University of South Carolina and Rice University has discovered just how to do it. The researchers were able to bridge a size gap, representing a wide chasm.

According to Hui Wang, a lead researcher and assistant professor of chemistry and biochemistry at South Carolina, metals such as silver, gold, platinum and palladium must be nanoparticles smaller than 5 nm to be effective nanocatalysts.

However, the 5 nm requirement falls below the size threshold that is needed to harness plasmon resonance, which is the basis of analytical techniques such as surface-enhanced Raman spectroscopy (SERS).

Two different etching methods produced two different kinds of nanoparticles; in both, the original flat surface of the cuboid was replaced by a curved surface. Courtesy of American Chemical Society.
Plasmonic activity can be harnessed for SERS and other analytical techniques to study catalytic reactions in great detail as they occur.

“Raman spectroscopy is extremely powerful [and] with information about molecular fingerprints, you can see the structures, you can tell how the molecules are oriented on the surface. And there is much more information [generated] with this approach,” Wang said, adding that the SERS approach allows for real-time monitoring of the reactions.

In order to utilize plasmon resonance’s analytical power, the nanoparticles must be “at least tens of nanometers in diameter,” according to Wang. He noted that the incompatibility of the nanomaterial sizes has prohibited the use of such spectral techniques in the past.

In their study, the researchers were able to combine both sizes via cuboidal nanoparticles that were about 50 nm wide and 120 nm long. Flat surfaces were chemically etched to generate curved surfaces.

The surface of the etched nanomaterial mimicked the environment of a sub-5 nm nanoparticle. And the researchers found that nanoparticles demonstrating plasmonic activity can be tuned by varying their shape and size.